The present invention relates to an improvement in a mechanical water pump of a type such that an impeller is rotated by a torque transmitted through a pulley and a pump shaft.
Such a water pump is suitably adapted to an engine to circulate an engine cooling water between the engine and a radiator by utilizing a torque of the engine.
In this type water pump, the pulley is fixed to one end of the pump shaft inserted in a pump housing, and the impeller is fixed to the other end of the pump shaft. Further, a water seal is provided on an intermediate portion of the pump shaft at a position adjacent to the impeller, so as to seal the cooling water from a pump chamber where the impeller is installed. Further, a bearing for rotatably supporting the pump shaft is provided between the pulley and the water seal in the pump housing.
In this type water pump, leakage of the water, particularly, a vapor of the water from the water seal cannot be completely avoided. As a result, the water vapor leaked from the water seal is dewed in an intermediate chamber defined by the pump housing, the bearing and the water seal, and the water dewed enters the bearing to cause deterioration of a grease or generation of rust, resulting in failure of the water pump.
To cope with this problem, there have been various structures in the prior art. For example, Japanese Utility Model Laid-open Publication No. 54-129003 discloses that the intermediate chamber defined by the pump housing, the bearing and the water seal is communicated through a ventilation hole to the outside of the pump housing. However, in this structure, the water vapor in the intermediate chamber cannot be positively ventilated, and the problem due to the water vapor cannot be accordingly avoided.
Japanese Utility Model Laid-open Publication Nos. 62-150596 and 63-146195 disclose that a partition disk is provided between the water seal and the bearing to prevent the water from reaching the bearing. However, in this structure, it is not possible to completely prevent the water from reaching the bearing. Accordingly, it is hard to avoid the deterioration of the grease or the like in the bearing for a long time.
Japanese Utility Model Laid-open Publication Nos. 63-146195, 56-76197, 61-103596 and 57-30400 disclose that a rotating fan is fixed to the pump shaft in the intermediate chamber between the water seal and the bearing to positively ventilate the water vapor in the intermediate chamber to the outside of the pump housing. However, in this structure, as the intermediate chamber is limited, an outer diameter of the rotating fan is obliged to be small. Accordingly, a ventilation efficiency is low.
Further, there is another problem such that a foreign matter such as mud or dust will enter the intermediate chamber from the ventilation hole to cause failure of the water seal or the bearing. To cope with this problem, Japanese Utility Model Laid-open Publication No. 63-150594 discloses that the ventilation hole opens to face a rear surface of the pulley seat, so as to prevent the foreign matter from directly entering the ventilation hole during running of a vehicle. However, in this structure, the ventilation of the water vapor in the intermediate chamber is not effected by the rotation of the pulley.
In consideration of the foregoing, Japanese Utility Model Laid-open Publication No. 63-146195 discloses that a ventilation hole communicated with the intermediate chamber opens to face the rear surface of the pulley seat and that a rotating fan having a large outer diameter is provided in the vicinity of the rear surface of the pulley seat so as to rotate with the pulley seat, so that an outside air can be positively fed from the ventilation hole into the intermediate chamber by utilizing the rotation of the pulley. According to this structure, the of the water vapor in the intermediate chamber can be effectively carried out by utilizing the rotating fan having a large outer diameter. However, the outer opening of the ventilation hole must be positioned to face the rear surface of the pulley seat. Accordingly, a degree of freedom of design of the water pump is limited. Furthermore, it has been found from a test result that the above structure of feeding the outside air into the intermediate chamber by utilizing the rotation of the pulley is lower in ventilation efficiency than a structure of sucking the intermediate chamber to the outside of the pump housing. Moreover, the conventional structures have a defect that the ventilation efficiency after stoppage of the rotation of the pulley is low.